MPs from Northern Ireland will be banned from sitting in the Stormont Assembly as well as Westminster, the government said on Sunday.

Northern Ireland Secretary Owen Paterson vowed to crack down on "double-jobbing" politicians who are paid to sit in Parliament as well as the devolved Belfast institution.

Speaking at the Conservative party conference in Manchester, Paterson said: "I don't believe anybody can be a full-time MP and a full-time Assembly Member, and so I will give you this commitment today – by agreement if possible, but by law if necessary – we will end double-jobbing."

Paterson praised the progress made in Northern Ireland over the past 20 years, but condemned the murder of PC Ronan Kerr in April, saying it showed why dissident republican terror groups like the Real and Continuity IRA wouldn't attract mainstream support.

He added: "The united response of the community to that atrocity demonstrated beyond words why these small groups of unrepresentative terrorists will never succeed."

Paterson said that now peace had largely returned to the six counties, it was time for Stormont to focus on rejuvenating Northern Ireland's economy.

"The next step is to move beyond the peace process and build a prosperous Northern Ireland in which everyone has a genuinely shared future," he said.

"We are living through very tough times, but we can't ignore the fact that as a result of Labour's legacy the United Kingdom as a whole is borrowing £232,000 a minute and Northern Ireland has to play its part in reducing the deficit.

"However, we have recognised Northern Ireland's special circumstances. That's why the reductions in the Executive's budget were less than the savings that many Whitehall departments have had to find.